Question: $\dfrac{9}{4} - \dfrac{9}{8} = {?}$
Answer: $ = {\dfrac{9 \times 2}{4 \times 2}} - {\dfrac{9 \times 1}{8 \times 1}} $ $ = {\dfrac{18}{8}} - {\dfrac{9}{8}} $ $ = \dfrac{{18} - {9}}{8} $ $ = \dfrac{9}{8}$